U.S. Pat. No. 4,869,818 discloses an orbital-type wastewater treatment system wherein an activated sludge or liquor is propelled around an elongated interior partition wall forming at least two parallel connected channels by a pump in the form of a vertical shaft provided with an aerator at an upper end and an impeller at a lower end. The pump is spaced from an end of the partition wall.
The orbital system of U.S. Pat. No. 4,869,818 represents an improvement in an orbital system 10, shown in FIG. 1 and known as a Carrousel® system, in which highly efficient aeration is provided by a series of low speed (about 25 to about 55 rpm) surface aerators 20, 21, 22 mounted at turning walls or communication sections 12, 14, 16 in a racetrack configuration formed by an outer tank wall 11, a series of partition walls 17, 18, 19 and additional turning walls 13, 15, normally all walls being constructed of concrete. The aerators act to provide mixed liquor mixing, aeration of the mixed liquor of waste water and activated sludge, and provide a plug flow of mixed liquor through the channels 28, 29 between the aerators and between either a partition and outer wall or between partitions. Residence times of 24 hours are common with the wastewater making dozens of cycles around the overall circuit. Turning vanes 23, 24 are also typically employed in the channels to improve hydraulic efficiency. Influent enters the system by pipe 9 at one or more of the surface aerators. Level of the mixed liquor is controlled by a motor controlled weir 25 which also functions to remove mixed liquor from the top surface of the system. Each orbital basin is custom designed based on individual design parameters such as influent quantity and characteristics, desired effluent levels, site size and shape, and population and industries served and to-be-served in the future.
FIG. 2 illustrates the improvement introduced into the Carrousel orbital system pursuant to the disclosure of U.S. Pat. No. 4,869,818. A mixed liquor pump includes an auxiliary radial flow submerged impeller 32 provided at or adjacent to an end of a shaft extension 31 underneath the surface aerator 30 and extending from the surface aerator shaft 43. The impeller 32 provides for additional pumping and resulting propulsion of the mixed liquor in the channels by reason of the location of the radial flow impeller with respect to a bottom end edge 40 of the partition wall 17 forming the particular channel. The vertical axis of the surface aerator and the radial impeller are generally approximately aligned with the longitudinal axis of its associated partition, i.e. the axis of impeller 32 and the longitudinal axis of wall 17, but may be slightly displaced. The lower radial flow impeller thus pumps mixed liquor in the same direction and directional manner as the surface aerator but a portion of the pumping energy is located adjacent to the tank or basin bottom 26. The basin may contain a deepened well area 36 which aids in the vertical mixing of mixed liquor by the surface aerator as shown by curved arrows 33. Dotted curved arrows show mixing behind the vertical partition 17 while straight dotted arrows 34 show the required velocity component resultant from the pumping action of both the surface aerator 30 and the lower radial flow impeller 32. The drive shaft 43 and the shaft extension 31 are rotatively driven together by motor 26 operating through a gear box 27 to provide the desired speed(s) of rotation. By reason of the additional lower impeller, the allowable basin depth is substantially increased by about at least 10% to 35% so that basin depths of from 2.5 to about 6.0 meters or greater can be utilized for the main channels 28, 29.